The present invention relates generally to a rolling element bearing for high-speed rotating equipment and, more particularly, to bearing assemblies and methods for retaining a bearing ball within a bearing assembly.
Various forms of ball retainers or cages for use with bearing balls exist. Many of these cages are annular members with pockets for separating and retaining the bearing balls. In operation of a bearing with such a cage, a ring, concentric with the cage, is driven to rotate the bearing balls and to drive the bearing balls in the direction of ring rotation. In turn, the bearing balls may engage the pockets to drive the cage or the cage may drive the bearing balls.
Ideally, there is substantially point contact between a bearing ball and the wall of a pocket in the direction of the movement of the cage. However, as the bearing balls move circumferentially, axial thrust loading combined with varying radial forces can cause the bearing balls to move away from an intended circumferential path (“excursions”). These excursions can lead to undesirable rolling resistance, non-uniform rotation and orbital velocities, and excessive wear of moving parts (such as bearing balls, raceways, and especially the cage). Additionally, due to mechanical imperfections, such as bearing ball imperfections and raceway imperfections, and system induced vibrations, the bearing balls also contact the wall of a cage pocket in an axial direction resulting in undesirable resistance to rolling movement, excessive cage forces, and instability of rotation.
U.S. Pat. No. 1,013,518 to Schilling appears to describe a cage ring for bearing balls. An elastic retaining ring, with an inner diameter larger than the inner diameter of the cage ring, is needed to retain the bearing balls. Because the retaining ring is elastic, large axial cage forces cannot be adequately reacted. The mean diameter of the retaining ring is larger than the pitch diameter of the bearing balls, making adequate reaction to large axial cage forces difficult. Furthermore, at high speeds, centrifugal forces acting on the large elastic retaining ring may exacerbate the tendency for portions of the cage to flare out radially. Such flaring may lead to rubbing of the cage against moving parts.
Another attempt to retain bearing balls is shown in U.S. Pat. No. 4,626,113 to Forknall ('113 patent). A plastic bearing ball cage is snapped together from two halves. No structure is shown for preventing the cage from snapping apart during operation. The bearing assembly of the '113 patent uses a ball-piloted cage, i.e., the bearing assembly is piloted (guided) by the bearing balls. A ball-piloted cage cannot accommodate ball excursions due to the small pocket clearance required to pilot the cage. As a result, the cage would undergo large ball pocket forces during high speed rotation of the bearing assembly.
As can be seen, there is a need for an improved apparatus and methods for retaining bearing balls in a bearing assembly such that excursions and other non-uniform movements of the bearing balls under high-speed rotation of the bearing assembly can be accommodated.